JP4467970B2 - X-ray computed tomography system - Google Patents

Description

  The present invention relates to a multitubular X-ray computed tomography apparatus.

  As is well known, in an X-ray computed tomography apparatus, an X-ray tube and an X-ray detector are arranged with a subject to be imaged in between. The X-ray tube collects projection data repeatedly at a constant period while continuously rotating around the subject together with the X-ray detector. Based on the projection data for 360 ° or 180 ° + fan angle, the cross section attenuation coefficient distribution, that is, the tomographic image is reconstructed.

  In recent years, with the reduction in size and weight of X-ray tubes and X-ray detectors, development of so-called multi-tube X-ray computed tomography apparatuses in which a plurality of X-ray tubes and X-ray detectors are mounted has progressed. Yes. By mounting a plurality of X-ray tubes and X-ray detectors, the time required to collect a set of projection data required to reconstruct a single tomographic image, that is, the scan time is shortened. Alternatively, the reconstruction resolution can be improved.

  By the way, in a conventional multi-tube X-ray computed tomography apparatus, X-rays are continuously generated from a plurality of X-ray tubes. Therefore, a situation occurs in which the scattered rays influence each other.

  An object of the present invention is to reduce the influence of scattered radiation in a multitubular X-ray computed tomography apparatus.

An aspect of the X-ray computed tomography apparatus according to the present invention includes a plurality of X-ray tubes, a plurality of X-ray detectors respectively corresponding to the plurality of X-ray tubes, and the plurality of X-ray tubes. A plurality of corresponding high voltage generation units, a plurality of data collection units respectively corresponding to the plurality of X-ray tubes, the plurality of X-ray tubes, the plurality of X-ray detectors, and the plurality of high voltage generations Pulse X-rays in order from the plurality of X-ray tubes and a plurality of X-ray tubes in order of approximately τ / n (τ; pulse duration, n; n = 2 ) and a control unit that controls the plurality of high voltage generation units so as to be generated by shifting each.

  According to the present invention, the influence of scattered radiation can be reduced.

  Hereinafter, an X-ray computed tomography apparatus (X-ray CT apparatus) according to the present invention will be described with reference to the drawings according to preferred embodiments. FIG. 1 shows the configuration of the main part of the X-ray computed tomography apparatus according to this embodiment. The X-ray computed tomography apparatus of this embodiment includes a scan gantry (also referred to as a gantry) 1, a computer device 3, and a multi-channel slip ring mechanism for electrically connecting the scan gantry 1 and the computer device 3. 2 is comprised. The scan gantry 1 is a component for collecting projection data relating to a subject, and the projection data is taken into the computer apparatus 3 and used for processing such as image reconstruction. The computer apparatus 3 has a system control unit 40 as a center, and a preprocessing unit 41, a data storage unit 42, an input unit 43, a display processor 44, a display unit 45, an image reconstruction unit via a data / control bus 48. 46 and a scan control unit 47 are connected.

  The scan gantry 1 is provided with a plurality of, here three, X-ray tubes 12, 22, and 32. Each of the three X-ray tubes 12, 22, 32 is provided with an X-ray diaphragm for defining the X-ray fan angle. As shown in FIG. 2, the three X-ray tubes 12, 22, and 32 are divided into an annular rotating frame 6, discretely along the circumference, typically 360 ° / tube number here. It is attached at regular intervals of 120 °. The rotating frame 6 is driven by the rotation driving unit 4 and is provided to rotate about the rotation axis RA. The X-ray tubes 12, 22, and 32 are independently supplied with a filament heating current and applied with a high voltage from the high voltage generators 11, 21, 31, and generate X-rays. The high voltage generators 11, 21, 31 are attached to the rotating frame 6. The high voltage generators 11, 21, and 31 typically rectify a 50/60 Hz AC power supply into a direct current, convert it to a high frequency alternating current of several kHz or more, boost it with a transformer, and then again A high-frequency inverter that is rectified and applied to the X-ray tubes 12, 22, and 32 is advantageous for downsizing. The high voltage generators 11, 21, 31 each independently receive a trigger pulse from the scan controller 47 and generate a high voltage pulse having a predetermined pulse duration τ (pulse width). High voltage pulses are applied between the cathode anodes of the corresponding X-ray tubes 12, 22, 32, respectively. The thermoelectrons generated in the cathode filament heated by the filament heating current are accelerated by the photovoltage and collide with the anode target to generate X-rays.

  A multi-channel X-ray detector 13, 23, 33 is mounted on the rotating frame 6 along with the X-ray tubes 12, 22, 32 and the high voltage generators 11, 21, 31. The X-ray detectors 13, 23, and 33 are attached to the rotating frame 6 at positions and orientations that face the X-ray tubes 12, 22, and 32, respectively. The outputs of the X-ray detectors 13, 23, and 33 are supplied to the preprocessing unit 41 of the computer apparatus 3 via the data collection units 14, 24, and 34, respectively. Each of the data collection units 14, 24, and 34 includes an IV converter that converts a current signal of each channel of the corresponding X-ray detector 13, 23, and 33 into a voltage, and the voltage signal as an X-ray exposure cycle. An integrator that periodically and synchronously integrates, an amplifier that amplifies the output signal of the integrator, and an analog / digital converter that converts the output signal of the preamplifier into a digital signal are provided for each channel.

  The preprocessing unit 41 corrects non-uniform sensitivity between channels for the data detected by the data collection units 14, 24, and 34, and the extreme signal intensity due to the strong X-ray absorber, mainly the metal part. Pre-processing such as correction of decrease in signal or signal dropout is executed. The projection data that has been corrected by the preprocessing unit 41 is stored in the data storage unit 42. The computer apparatus 3 includes a pre-processing unit 41 and a data storage unit 42, a system control unit 40, an input unit 43 having a keyboard and a mouse, a display processor 44, a display unit (CRT or panel display) 45, and an image reconstruction unit 46. The scan control unit 47 is configured.

  The scan control unit 47 supplies a rotation control signal to the rotation drive unit 4 in order to stably rotate the rotating frame 6 at a constant speed during scanning (data collection), and from each of the X-ray tubes 12, 22, 32. In order to generate X-ray pulses one after another, trigger pulses are sequentially supplied to the high voltage generators 11, 21, 31, and further, in synchronization with the generation of X-ray pulses, data acquisition cycles (charge accumulation, signal charge readout, In order to repeat (reset), a trigger pulse or a signal obtained from the trigger pulse is supplied to the data collection units 14, 24, and 34.

  In the present embodiment, the scan control unit 47 is selectively equipped with three types of modes (referred to as pulse modes) for generating X-ray pulses from the X-ray tubes 12, 22, and 32. The three types of pulse modes can alleviate the influence of scattered radiation compared to the case of continuous X-rays. The first pulse mode (referred to as the scattered radiation removal priority mode) eliminates scattered radiation. The second pulse mode (referred to as the XY resolution priority mode) has a characteristic that “XY resolution” is high, although the scattered radiation reduction effect is slightly lower than that of the first scattered radiation removal priority mode. is doing. High XY resolution means that the number of viewpoints (also referred to as sampling points) for collecting data during one rotation is large and the interval between viewpoints (view pitch) is narrow. The third mode (scan speed priority mode) is a mode that can increase the scan speed to half that of the scattered radiation removal priority mode and the XY resolution priority mode with an XY resolution equivalent to that in the scattered radiation removal priority mode. It is.

  As shown in FIG. 3, the scan mode (single slice / multi-slice / helical), scan position, CTDI (CT dose index representing exposure dose), tube voltage via the input unit 43 by the operator at the scan planning stage. In addition to scan conditions such as (kV), tube current (mA), and scan speed (time required for one rotation), a scattered radiation removal priority mode, an XY resolution priority mode, and a scan speed priority mode are selected for each scan project. In any mode, pulse X-rays are sequentially generated from the plurality of X-ray tubes 12, 22, and 32 by shifting by approximately τ / n (τ: pulse duration, n: positive real number). As a result, the influence of scattered radiation can be removed or reduced. Although details will be described later, n = 1 is set in the scattered radiation removal priority mode, and n = 2 is set in the XY resolution priority mode and the scan speed priority mode.

  FIG. 4 shows the generation timing of pulse X-rays in the scattered radiation removal priority mode. In the scattered radiation removal priority mode, the scan control unit 47 causes the high voltage generation units 11, 21, 31 to generate pulse X-rays from the X-ray tubes 12, 22, 32, as shown in FIG. Each generates a trigger pulse. Here, for convenience of explanation, the pulse duration (pulse width) τ of the pulse X-ray is assumed to be constant. Pulse X-rays are repeatedly generated from the first X-ray tube 12 at a constant period C1. The period C1 is set to pulse duration τ × tube number N, here 3 · τ. Similarly, pulse X-rays are repeatedly generated from the second and third X-ray tubes 22 and 32 with a constant period C1.

  The generation time of the pulse X-ray from the second X-ray tube 22 is delayed by the delay time Δt with respect to the generation time of the pulse X-ray from the first X-ray tube 12. This delay time Δt is set approximately equivalent to the pulse duration τ. The generation time of the pulse X-ray from the third X-ray tube 32 is substantially equivalent to twice the pulse duration τ with respect to the generation time of the pulse X-ray from the first X-ray tube 12. And is delayed by a time approximately equivalent to the pulse duration τ with respect to the generation timing of the pulse X-rays from the second X-ray tube 22.

  A scan is performed so that charges are accumulated in the first X-ray detector 13 in synchronization with the duration of the pulse X-rays from the first X-ray tube 12, and the charge readout and reset are performed following the charge accumulation period. The control unit 47 controls the operation of the first data collection unit 14. Similarly, charges are accumulated in the second and third X-ray detectors 23 and 33 in synchronization with the duration of the pulse X-rays from the second and third X-ray tubes 22 and 32, and the charge is accumulated. The scan control unit 47 controls the operations of the second and third data collection units 24 and 34 so that charge reading and reset are performed following the period.

  Due to the generation control of the pulse X-rays, the pulse X-rays are generated from the first X-ray tube 12 during the charge accumulation period of the first X-ray detector 13, and the second and third X-ray tubes are generated. Pulse X-rays are not generated from the spheres 22 and 32. Therefore, the first X-ray detector 13 does not detect scattered radiation derived from the pulse X-rays from the second and third X-ray tubes 22 and 32. The effect of scattered radiation can be almost completely eliminated.

  Similarly, during the charge accumulation period of the second X-ray detector 23, pulse X-rays are generated from the second X-ray tube 22 and pulses X from the first and third X-ray tubes 12 and 32. No line is generated. Therefore, the second X-ray detector 23 does not detect scattered radiation derived from the pulse X-rays from the first and third X-ray tubes 12 and 32.

  During the charge accumulation period of the third X-ray detector 33, pulse X-rays are generated from the third X-ray tube 32, and pulse X-rays are generated from the first and second X-ray tubes 12, 22. Not. Therefore, the third X-ray detector 33 does not detect scattered radiation derived from the pulse X-rays from the first and second X-ray tubes 12 and 22.

  In this way, by shifting the generation timing of the pulse X-rays by the pulse duration τ, the situation where the scattered rays influence each other is avoided. In the above description, the delay time Δt of the pulse X-ray from the second X-ray tube 22 with respect to the pulse X-ray from the first X-ray tube 12 and the pulse X from the second X-ray tube 22 are further described. The delay time Δt of the pulse X-ray from the third X-ray tube 32 with respect to the line is set to be approximately equivalent to the pulse duration τ, but may be set to pulse duration τ + predetermined margin time α. Thereby, the period C1 is set to 3 · τ + 3 · α. Even if slight fluctuations occur in the rise and fall times of the pulse X-ray by giving the margin time α to the delay time, the first, second, and third X-ray tubes 12, 22, and 32 The overlap of pulse X-rays can be avoided.

  FIG. 5 shows pulse X-ray generation timing in the XY resolution priority mode. In the XY resolution priority mode, the scan controller 47 causes the high voltage generators 11, 21, 31 to generate pulsed X-rays from the X-ray tubes 12, 22, 32, as shown in FIG. Each trigger pulse is generated. As described above, the pulse duration time (pulse width) τ of the pulse X-ray is assumed to be constant. Pulse X-rays are repeatedly generated from the first X-ray tube 12 at a constant period C2. The period C2 is set shorter than the period C1 in the above-described scattered radiation removal priority mode, and is set to N · (τ / 2) where N is the number of tubes. Similarly, pulse X-rays are repeatedly generated from the second and third X-ray tubes 22 and 32 with a constant period C2.

  The period C2 (= N · (τ / 2)) in the XY resolution priority mode can be shortened to ½ of the period C1 (= N · τ) in the scattered radiation removal priority mode. Therefore, the XY resolution (the number of viewpoints per rotation) in the XY resolution priority mode can be improved to twice that in the scattered radiation removal priority mode under the condition that the scan speed is the same. it can.

  The generation time of the pulse X-ray from the second X-ray tube 22 is substantially equivalent to ½ of the pulse duration τ with respect to the generation time of the pulse X-ray from the first X-ray tube 12. Is set. The generation time of the pulse X-ray from the third X-ray tube 32 is delayed by a time substantially equivalent to the pulse duration τ with respect to the generation time of the pulse X-ray from the first X-ray tube 12. Further, the pulse X-ray generation time from the second X-ray tube 22 is delayed by a time substantially equivalent to ½ of the pulse duration τ. Further, returning to the generation timing of the pulse X-ray from the third X-ray tube 312, the generation time of the pulse X-ray from the first X-ray tube 12 is ½ of the pulse duration τ. Is delayed by an approximately equivalent time.

  Charges are accumulated in the first, second and third X-ray detectors 13, 23 and 33 in synchronization with the duration of the pulse X-rays from the first, second and third X-ray tubes 12, 22 and 32. The scan control unit 47 controls the operations of the first, second, and third data collection units 14, 24, and 34 so that charge reading and reset are performed following the charge accumulation period.

  With such generation control of pulse X-rays, pulse X-rays are generated from the third X-ray tube 32 in the first half of the charge accumulation period of the first X-ray detector 13, but the second X-ray tube No pulse X-ray is generated from the sphere 22. In the second half of the charge accumulation period of the first X-ray detector 13, pulse X-rays are generated from the second X-ray tube 22, but no pulse X-rays are generated from the third X-ray tube 32. Therefore, the first X-ray detector 13 has a scattered dose that is higher than that of the conventional case where the first X-ray detector 13 receives scattered radiation derived from pulsed X-rays from the second and third X-ray tubes 22 and 32 throughout the charge accumulation period. In principle, it can be reduced to 1/2.

  Similarly, in the first half of the charge accumulation period of the second X-ray detector 23, pulse X-rays are generated from the first X-ray tube 12, but pulse X-rays are generated from the third X-ray tube 32. Not generated. In the second half of the charge accumulation period of the second X-ray detector 23, pulse X-rays are generated from the third X-ray tube 32, but no pulse X-rays are generated from the first X-ray tube 12. Therefore, the second X-ray detector 23 has a scattered dose higher than that in the conventional case where the second X-ray detector 23 receives scattered radiation derived from pulsed X-rays from the first and third X-ray tubes 12 and 32 over the entire charge accumulation period. In principle, it can be reduced to 1/2.

  Similarly, in the first half of the charge accumulation period of the third X-ray detector 33, pulse X-rays are generated from the second X-ray tube 22, but pulse X-rays are generated from the first X-ray tube 12. Not generated. In the second half of the charge accumulation period of the third X-ray detector 33, pulse X-rays are generated from the first X-ray tube 12, but no pulse X-rays are generated from the second X-ray tube 22. Therefore, the third X-ray detector 33 has a scattered dose that is higher than that of the conventional case where the third X-ray detector 33 receives scattered radiation derived from pulsed X-rays from the first and second X-ray tubes 12 and 22 over the entire charge accumulation period. In principle, it can be reduced to 1/2.

  In the scan speed priority mode, pulse X-ray generation and signal acquisition control are the same as those in the XY resolution priority mode shown in FIG. 5, but the time required for one rotation of the rotating frame 6, that is, the scan speed, removes scattered radiation. The speed is increased to about 1/2 times that of the priority mode and the XY resolution priority mode. Thereby, in the scan speed priority mode, the XY resolution is equivalent to that of the scattered radiation removal priority mode of FIG. 4, and the scan speed can be increased to ½. In the scan speed priority mode, the pulse X-ray generation and signal acquisition control are the same as the XY resolution priority mode shown in FIG. 5, and therefore, the scattered radiation reduction effect equivalent to that in the XY resolution priority mode can be achieved.

  As described above, according to the present embodiment, the influence of scattered radiation can be eliminated or reduced in the multitubular X-ray computed tomography apparatus. In the case of reducing the influence of scattered radiation, the XY resolution can be improved approximately twice or the scanning speed can be increased compared to the case of eliminating the influence of scattered radiation. These modes can be used effectively according to the movement and size of the subject.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

The block diagram of the principal part of the X-ray computed tomography apparatus which concerns on embodiment of this invention. The figure which shows arrangement | positioning of the three X-ray tubes of FIG. The figure which shows the example of a scan plan setting screen in this embodiment. The figure which shows the timing shift amount of the pulse X-ray at the time of a scattered radiation removal priority in this embodiment. The figure which shows the timing shift amount of the pulse X-ray at the time of XY resolution priority in this embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Gantry, 4 ... Rotation drive part, 5 ... Bed drive part, 10 ... 1st X-ray system, 11 ... 1st high voltage generation part, 12 ... 1st X-ray tube, 13 ... 1st X-ray detector, 14 ... First data collection unit, 20 ... second X-ray system, 21 ... second high voltage generation unit, 22 ... second X-ray tube, 23 ... second X-ray detector, 24 ... second data collection unit, 30 ... 3X Line system 31 ... third high voltage generator 32 ... third X-ray tube 33 ... third X-ray detector 34 ... third data collection unit 2 ... slip ring mechanism 3 ... computer device 40 ... system Control part 41 ... Pre-processing part 42 ... Data storage part 43 ... Input part 44 ... Display processor 45 ... Display part 46 ... Image reconstruction part 47 ... X-ray control part.

Claims (3)

A plurality of X-ray tubes;
A plurality of X-ray detectors respectively corresponding to the plurality of X-ray tubes;
A plurality of high voltage generators respectively corresponding to the plurality of X-ray tubes;
A plurality of data collection units respectively corresponding to the plurality of X-ray tubes;
A substantially annular frame rotatably mounted on which the plurality of X-ray tubes, the plurality of X-ray detectors, the plurality of high voltage generation units, and the plurality of data collection units are mounted;
The plurality of high voltage generators are controlled so that pulse X-rays are generated in order from the plurality of X-ray tubes, shifted by approximately τ / n (τ; pulse duration, n; n = 2 ). An X-ray computed tomography apparatus comprising: a control unit. A plurality of X-ray tubes;
A plurality of X-ray detectors respectively corresponding to the plurality of X-ray tubes;
A plurality of high voltage generators respectively corresponding to the plurality of X-ray tubes;
A plurality of data collection units respectively corresponding to the plurality of X-ray tubes;
A substantially annular frame rotatably mounted on which the plurality of X-ray tubes, the plurality of X-ray detectors, the plurality of high voltage generation units, and the plurality of data collection units are mounted;
The plurality of high voltage generators are controlled so that pulse X-rays are sequentially shifted from each of the plurality of X-ray tubes by approximately τ / n (τ; pulse duration). An X-ray computed tomography apparatus comprising: a control unit that selectively sets the n to either 1 or 2 according to an instruction from a person . A plurality of X-ray tubes;
A plurality of X-ray detectors respectively corresponding to the plurality of X-ray tubes;
A plurality of high voltage generators respectively corresponding to the plurality of X-ray tubes;
A plurality of data collection units respectively corresponding to the plurality of X-ray tubes;
A substantially annular frame rotatably mounted on which the plurality of X-ray tubes, the plurality of X-ray detectors, the plurality of high voltage generation units, and the plurality of data collection units are mounted;
The plurality of high voltage generators so that the pulse X-rays are generated in order from the plurality of X-ray tubes with a shift of approximately τ / n (τ; pulse duration, n; n is a real number greater than 1 ). And an X-ray computed tomography apparatus characterized by comprising:

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